The present invention relates to a process for manufacturing cold-formed shaped forms of packaging from a metal-plastic laminate in which the laminate is held between a retaining tool and a die exhibiting at least one opening, and a stamp is driven into the die opening causing the laminate to be formed into a shaped form of packaging featuring one or more recesses. The present invention relates also to a device for performing the process of cold forming a metal-plastic laminate into a shaped form of packaging.
It is known to manufacture shaped forms of packaging such as e.g. base parts for blister packs, also known as push-through packs, or other forms of packaging e.g. by deep drawing, stretch-drawing or thermoforming. The shaped packaging may be manufactured from thermoplastics or from composites or laminates such as e.g. aluminum foils and plastic films or extruded layers of thermoplastics.
If the packaging is made of laminates containing metal foils, then shaping tools comprising a stamp, a die and a retaining tool may be employed for its manufacture. As it is being deformed, the laminate is clamped securely between the die and the retaining tool, and the stamp moved towards the laminate. As it is lowered, the stamp moves deeper into the openings in the die thereby deforming the laminate. In that process the flat laminate is converted into a shaped part exhibiting one or more recesses which are surrounded by shoulders corresponding to the original flat plane of the laminate. Only that part of the laminate in the region of the die opening can flow or be stretched to form a shaped part. Adequate lateral distance must be maintained between the stamp and the die opening in order that the laminate, especially laminates containing metal foil, can be deformed without cracks and pores forming. If the laminate contains a metal foil, only recesses of small sidewall height can be achieved by this cold forming process. The result is poor drawing ratios i.e. shallow recesses of large diameter and, therefore, forms of packaging which are too large in relation to the contents.
One possibility for obtaining more laminate for shape-forming purposes may be to reduce the retaining force and to employ deep drawing methods. However, folds would form in the edge or shoulder regions, and so this type of technology may not be used e.g. for making blister packs from laminates containing metal foil. The edge region and, if desired, the shoulder region of shaped forms of packaging are normally employed for sealing on the lid. If there were folds present there, however, then it would not be possible to seal the edge and shoulders.
The object of the present invention is to describe a process which enables shaped forms of packaging, or shaped parts, to be made from laminates containing metal foil by means of cold forming whereby the forms of shaped packaging so produced are free of folds, and the recesses exhibit large wall height.
That objective is achieved by way of the invention in which a the die and the retaining tool feature a facing edge region and the die, within the edge region, features a shoulder region that surrounds the die opening or openings, and the surface of the shoulder region lies 0.1 to 10 mm lower than the surface of the edge region of the die, and a first stamp or stamps, featuring a high friction, pre-forms the metal-plastic laminate in one or more steps up to 100% of the final depth of the recess, and subsequently a second stamp or stamps, featuring a low friction forming surface forms the pre-formed metal-plastic laminate in one or more steps to at least 100% of the final depth of the recess.
In the present invention the various stamps are advantageously employed one after the other and, in a series of steps down maximum depth via pre-forming, each stamp is lowered into the die opening by the same amount or further than the preceding stamp. As the metal-plastic laminate springs back, at least the last forming step must exceed the full, desired depth of deformation.
In a useful version of the invention the stamp is driven in a first step or steps down to 90%, especially usefully to 70% and advantageously to 50% of the final depth of the recess, and in a second step or steps is driven down to 100-115%, advantageously 103-110% of the final depth of the recess.
Usefully, the stamps or stamping tools, which exhibit a high friction forming surface and are employed in the first step or steps, are cylindrical, blunted cone, blunted pyramid or barrel shaped. The stamps employed for the second step or steps have the shape of a cone, pyramid, blunted cone, blunted pyramid, segment of a sphere or cap. The stamps for the first step feature in particular vertical or steep sidewalls, and the edge or periphery at the bottom of the stamp has a small radius. The lower friction surface stamp for the second step, may be vertical or less steep and in particular exhibit sloping sidewalls, and the transition to the bottom of the stamp may be rounded or roundish in shape. This enables the metal-plastic laminate to slide only poorly over the edge or periphery between the sidewall and bottom of the stamp so that the metal-plastic laminate material from other regions is deformed first, then in a second step or steps, because of the low friction and the rounded shape of the stamp, the metal-plastic laminate material from the bottom region of the stamp is also deformed.
In a second useful version the stamp with a high friction forming surface in contact with the laminate may exhibit higher friction than the stamp with a low friction forming surface.
The process according to the invention be performed e.g. using a die and retaining tool and two or more stamps which are lowered one after the other into the openings in a die then raised again. On their surfaces that effect forming the stamps or stamping tools exhibit different degrees of friction. For pre-forming a first stamp with high friction forming surface is employed; this tool is then withdrawn and a second stamp with low friction forming surface performs the final shape-forming in the same die. Likewise, one may employ three or more stamps with forming surfaces of two different degrees of friction or gradually smaller degrees of friction.
The process may be advantageously performed in such a manner that the stamps are arranged coaxially or telescopically inside each other. A first stamp, featuring in particular a low friction forming surface and ring-shaped in plan view, can effect pre-forming by lowering it into the die. The first stamp may be left in the pre-forming position and a second cylindrical-shaped stamp which slides telescopically in the first ring-shaped stamp and exhibits a high friction forming surface, is then lowered effecting the final forming of the laminate. Such stamping tools may be made up of two or more ring-shaped stamping tools and an innermost cylindrical stamping tool all of which slide telescopically inside each other. The degree of friction of the surfaces effecting forming may decrease gradually from a high degree of friction on the outermost stamping tool to a low degree of friction on the innermost stamping tool, usefully at least in two steps.
The process may also be performed preferably in such a manner that several dies, in particular two dies with their retaining tools, are arranged one after the other and with a stamp appointed to each die. Correspondingly, with two dies and their appointed stamps arranged one after each other, the surface of the first stamp that effects forming may exhibit high friction, the second stamp low friction. Working at a set rhythm the laminate is pre-formed in a first step in the first die, then formed to the final shape in a second step in the second die. It is also possible to perform the pre-forming in two or more steps and to divide the final shaping operation into two or more steps, with the result that the total number of steps in the process used is three, four etc., etc., whereby the friction may be reduced in two steps or gradually in the course of the individual steps.